B. de Groot

Extreme hydrogen plasma densities achieved in a linear plasma generator

A magnetized hydrogen plasma beam was generated with a cascaded arc, expanding in a vacuum vessel at an axial magnetic field of up to 1.6T. Its characteristics were measured at a distance of 4cm from the nozzle: up to a 2cm beam diameter, 7.5×1020m−3 electron density, ∼2eV electron and ion temperatures, and 3.5km∕s axial plasma velocity. This gives a 2.6×1024H+m−2s−1 peak ion flux density, which is unprecedented in linear plasma generators. The high efficiency of the source is obtained by the combined action of the magnetic field and an optimized nozzle geometry. This is interpreted as a cross-field return current that leads to power dissipation in the beam just outside the source.

Magnum-psi, a new linear plasma generator for plasma-surface interaction studies in ITER relevant conditions

The Magnum-psi project (magnetised plasma generator and numerical modelling for plasma-surlface interaction) aims at the fundamental study of plasma-surface interaction processes in conditions relevant to the ITER divertor. A linear plasma generator has been constructed in which a hydrogen ion flux of 10 23 particles/m 2 s to a surface can be realised, at a temperature of around 1 eV. A longitudinal magnetic field of I 0 cm and a controlled temperature in the range 0.1-10 eV.

PSI research in the ITER divertor parameter range at the FOM PSI-lab

FOM-Rijnhuizen is building, in cooperation with its Trilateral Euregio Cluster (TEC) partners, a PSI-laboratory to study plasma surface interaction (PSI) under extreme, ITER relevant plasma conditions. The largest linear plasma generator of PSI-lab is Magnum-PSI, and is designed to deliver up to 10 MW m−2 power over a 10 cm diameter hydrogen plasma beam with an electron density (ne) up to 1021 m−3 and electron-temperature (Te) between 1–5 eV. Magnum-PSI is presently under construction and its predesign is presented. Its forerunner is Pilot-PSI, in which record plasma parameters of ne=4×1021 m−3 at Te=2 eV in a ~1 cm wide hydrogen beam confined by a magnetic field (B) ≤1.6 T were measured at 40 mm downstream the source nozzle. At 17 mm in front of a target (located at 0.56 m distance from the source nozzle), ne>1021 m−3 and Te≤ 4 eV have been demonstrated. Initial experiments on exposing fine-grain carbon samples are presented that showed up to 20 μm s−1 erosion as a demonstration of the extreme plasma conditions. Spectroscopy was applied to compare chemical erosion yields for flux densities up to 5.0×1024 m−2 s−1.

High-temperature, high-beta plasma heating by weak turbulence in the TORTUR tokamak

Abstract Results with high-temperature, high-beta plasmas obtained in the TORTUR tokahak by operation in a weakly turbulent discharge regime are described and compared with normal classical discharges. In turbulent regimes axial electron and ion temperatures f more than 1000 eV are obtained together with beta poloidal values up to 4. Temperatures and densities scale proportionally to the current.

A 3 T magnet system for MAGNUM-PSI

The FOM-Institute for Plasma Physics is preparing the construction of Magnum-psi, a magnetized (3 T), steady-state, large area (100 cm/sup 2/), high-flux (up to 10/sup 24/ H/sup +/ ions m/sup -2/s/sup -1/) plasma generator. Magnum-psi will be used to study plasma-surface interaction in conditions similar to those in the divertor of ITER and fusion reactors beyond ITER. The active magnetic field region is required to be 4 meter long, 1 meter diameter and steady state. This, together with the need for minimization of the running costs, makes the application of superconducting coils imperative. The magnet system will be unique because of its maximum transparency to provide optimal radial access to the experimental region inside the magnet bore. In this contribution we present a magnet configuration that consists of 5 cylindrical, conduction cooled NbTi coils. These generate an axial field of 3 T with a maximum field on the coils below 6 T. Two cryogenic structures are proposed: the discrete coils are either placed within separate cryostats or are supported by a single cylinder in a shared cryostat with 32 room temperature view ports. Room temperature iron rings close to the outer coils reduce the axial forces that would otherwise put severe constraints on the mechanical structure. The field will most probably be passively shielded by an iron dome at 2 meters from the cryostat.

Plasma confinement and skin currents in a small tokamak with turbulent heating

Abstract Results on plasma confinement, heating, suprathermal radiation and overall conductivity together with the time development of radial current density profiles during current-driven turbulence in the toroidal device “TORTUR” are reported.

Current drive and mode stabilization experiments with real-time control of the gyrotron output power

Abstract Real-time control of the gyrotron output power has been obtained by controlling the gyrotron cathode voltage. This control system has been used to explore feedback control of global and local plasma parameters. A description is given of technical set-up and of the results, which include control of the electron temperature Te with excellent time response and successful stabilization of m/n=2/1 modes in case of cw injection.

Multiple discharge channels in a cascaded arc to produce extreme hydrogen plasma beams

A high flux cascaded arc hydrogen plasma source is being developed for the linear plasma generator Magnum-PS I (magnetised plasma generator and numerical modeling for plasma surface interaction studies). Magnum-PSI will be the heart of the PSI-lab at the FOM-Institute for Plasma Physics Rijnhuizen and is being developed to investigate PSI issues for ITER. Especially the wall material of the so-called divertor of ITER, which is the region where plasma and impurities are neutralized and pumped off, will receive unprecedented particle and power loads. The expected numbers are: particle fluxes of up to 1024 ions/m2s and power loads of up to 10 MW/m2. We have demonstrated that it is possible to produce such conditions in a linear plasma generator with a cascaded arc in a magnetic field of 1.6 T2. The diameter of the plasma beam in these experiments was typically 20 mm. For Magnum-PSI, we envisage a beam diameter of 10 cm in order to enter the strongly coupled regime of PSI research. In this contribution we investigate the production of larger beam diameters by combining the output of several discharge channels. A new arc consisting of three separate arc channels with a common cylinder anode was constructed for this purpose. Thomson scattering, high resolution Doppler spectroscopy and calorimetry were applied to measure the performance of and interaction between the three channels.